Dynamic Trading and Asset Prices: Keynes vs. Hayek

We investigate the dynamics of prices, information and expectations in a competitive, noisy, dynamic asset pricing equilibrium model. We look at the bias of prices as estimators of fundamental value in relation to traders' average expectations and note that prices are more (less) biased than average expectations if and only if traders over- (under-) rely on public information with respect to optimal statistical weights. We find that prices are biased in relation to average expectations whenever traders speculate on short-run price move- ments. In a market with long term traders, over-reliance on public information obtains if noise trade increments are correlated enough and/or there is low enough residual uncertainty in the payoff. This defines a “Keynesian” region; the complementary region is “Hayekian” in that prices are less biased than average expectations in the estimation of fundamental value. The standard case of no residual uncertainty and noise trading following a random walk is on the frontier of the two regions. With short-term traders there typically are two equilibria, with the stable (unstable) one displaying over- (under-) reliance on public information.